A conventional box wrench is shown in FIG. 9 and generally includes a first driving head 40 which is a box end at an end of the handle and multiple protrusions 41 extending from the inside of the box end 40, and a second driving head 42 which is an open end is connected to the other end of the handle. When rotating the bolts of a piping system, the first driving head 40 cannot be used so that the user has to switch the wrench to the second driving head 42, and this is not convenient for the user.
In order to improve the shortcoming of the conventional wrench as shown in FIG. 9, another wrench as shown in FIGS. 11 to 12 is provided and includes an opening 52 defined in a side of the box end driving head 50 which has protrusions 51 extending from the inside thereof so as to be used to the bolts of the piping system. However, the opening 52 reduces the strength of the box end driving head 50 and the maximum torque that the wrench can output is reduced. The two jaws of the driving head 50 may be expanded outward.
In order to improve the shortcoming of the conventional wrench as shown in FIGS. 10 to 12, yet another wrench as shown in FIG. 13 is provided and includes a thickened base at the connection between the C-shaped driving head 60 and the handle 61. As shown in FIG. 14, the outer periphery of the top surface 62 and the bottom surface 620 of the C-shaped driving head 60 are located on an oval 64 which tangents a standard circle at a point “E” so that the length of the wrench does not need to be increased and the symmetric principle is maintained. However, the thickened area has to be located at the connection between the C-shaped driving head 60 and the handle 61, the thickness of the jaws 66 beside the opening 65 cannot be increased. Therefore, the shortcoming of the outward expanding of the jaws is not improved.